There is a need in the field of medical insertion devices to provide a slippery yet medically safe surface so that the device can easily be inserted into the human body without causing injury, infection, or excessive discomfort. Usually, the medical insertion device has a guide portion which is inserted into the body first, and whose surface should be exceptionally slippery when wet. The guide portion surface must minimize friction between the guide portion and the inside of the vein or organ, and must also be non-toxic and otherwise chemically inert when exposed to bodily fluids.
Various means for minimizing the surface friction of the guide portions of medical devices are known. U.S. Pat. No. 5,835,003 issued to Becker et al., discloses a medical tubing whose exterior is at least partially covered with a water-activated lubricating coating of a hydrophilic (i.e. water absorbing) thermoplastic resin which is adhesively compatible with the material of the medical tubing. The reference specifically discloses the use of a thermoplastic hydrophilic polyurethane resin. A quantity of polyvinyl pyrrolidone having a molecular weight of at least 200,000 is intimately dispersed and forms a separate phase in the hydrophilic polyurethane. When the coating becomes wet, the hydrophilic polyurethane swells and the polyvinyl pyrrolidone bleeds to the surface to form a lubricating film on the guide portion of the medical device.
U.S. Pat. No. 4,997,901, issued to Ofstead, also discloses medical devices coated with a hydrophilic polymer and lists polyvinyl alcohol which is more than about 88% hydrolyzed, as the preferred hydrophilic polymer.
U.S. Pat. No. 4,884,579, issue to Engelson, discloses a catheter guide wire and lists several polymers that can be used as cover materials to provide a low friction surface. Two of the cover materials listed are polyurethane and polyvinyl pyrrolidone.
U.S. Pat. No. 4,729,914, issued to Kliment et al., discloses the application of N-vinyl pyrrolidone copolymers to a substrate having free isocyanate groups. A chemical reaction then occurs between the N-vinyl pyrrolidone and the isocyanate groups of the substrate, causing the formation of a chemically linked polyvinyl pyrrolidone which has less tendency to leach.
U.S. Pat. No. 4,682,607, issued to Vaillancourt et al., discloses a wire guide provided with a polymer coating which can be a hydrophilic material such as polyvinyl pyrrolidone, polyurethane or hydroxyethyl methacrylate.
European Patent Application 0 405 823A2 discloses generally the use of a hydrophilic coating on the outside surface of a guide wire, to reduce friction.
One of the disadvantages of hydrophilic coatings known in the art is that they tend to leach and can become easily separated from the substrate. Separation can be prevented to some extent by providing for a chemical reaction between the coating and substrate to anchor the hydrophilic coating to the substrate. However, this creates the additional risk that quantities of undesirable, unreacted chemicals will be present in the coating. Thus, there is a need to improve adhesion between hydrophilic coatings and substrates without using a chemical reaction.